The present invention relates to a transmission apparatus, and more particularly, to a transmission apparatus which includes a compound planetary gear set, and is capable of achieving a multi-stage variable-speed rotation with a simple structure and performing a stopping and opening operation.
Recently, in developing an electric vehicle, a development of an in-wheel driving system is proceeded to increase energy efficiency and an inner space of a vehicle body and to obtain a production cost-reduction effect according to modularization. An electric motor is more suitable for a driving of the vehicle due to speed-torque characteristics thereof, comparing with an engine. However, since energy efficiency thereof is deteriorated in low speed and high speed regions, there is a problem that, when the electric motor is operated in these regions, the efficiency is lowered, and heat is severely generated. Therefore, when a mechanical transmission apparatus is used with the motor, it is possible to increase performance of the electric vehicle. However, since the transmission apparatuses developed till now have a complicated structure, a large size and an axially long structure, it is difficult to be installed in a vehicle wheel together with the motor. In the case of the vehicle wheel, since it should perform a high torque low speed rotation and a low torque high speed rotation as well as a braking operation and an opening operation which allows a person to push the vehicle, there is another problem that, when an existing transmission apparatus is used, it is difficult to install the apparatus in the wheel.